Thin Film of Poly-peri-naphthalene (PPN) Fabricated by Direct Laser Writing and Its Use for Humidity Sensing

Inspired by the versatility of the direct laser writing carbonization (DLWc) technique as well as the metal-ion-assisted coordination polymer of 3,4,9,10-perylene tetracarboxylic dianhydride (PTCDA), in the present study, we present a DLWc-enabled approach for cost-effectively fabricating a poly-peri-naphthalene (PPN) thin film with the advantages of patternability, environmental benignity, and scalability. Optical and scanning electron microscopy, as well as ultraviolet-visible-near-infrared, Fourier transform infrared, Raman, and X-ray photoelectron spectroscopies, were performed to confirm that the spray-coated thin film of the Mg-PTCDA coordination polymer can be in situ converted into a PPN thin film upon CO₂ laser irradiation. The effects of the laser power and Mg²⁺ concentration on the structure and electrical properties of the laser-processed PPN thin films were investigated. Lastly, we demonstrated that the laser-processed PPN thin films can be used for humidity sensing with characteristics of a rapid response time and excellent hysteresis. It is expected that this new method for fabricating PPN thin films will lead to a wide range of applications of PPN in the fields of sensing, electronics, and energy storage.